Spong, in U.S. Pat. No. 4,097,895 which issued June 27, 1978, has disclosed an ablative optical recording medium for use in an optical recording system, which medium comprises a light reflective material which is coated with a layer of a light absorptive organic material. A focused, modulated light beam, such as a light beam from an argon ion laser, when directed at the recording medium, vaporizes or ablates the light absorptive layer, leaving an opening in this layer and exposing the light reflecting material. The thickness of the light absorptive layer is chosen so that the reflectivity of the recording medium is reduced.
Bell, in a co-pending application, Ser. No. 054,437 filed July 3, 1979, which is a continuation of Ser. No. 782,032 filed Mar. 28, 1977, now abandoned, has disclosed an improved ablative trilayer optical recording medium for use in the Spong optical recording system. The trilayer optical recording medium comprises a light reflective material, a layer of a light transmissive material overlying the light reflective material and a layer of a light absorptive material overlying the light transmissive layer. The thickness of the light absorptive layer is so related to the thickness of the light transmissive layer and the optical constants of the light reflective material and the transmissive and absorptive layers, so as to reduce the optical reflectivity of the recording medium. A maximum fraction of light impinging on the recording medium from a focused, modulated light beam, is then absorbed and converted to thermal energy in the light absorbing layer. The thermal energy ablates or melts the light absorptive layer producing an opening in the layer and thus exposing the underlying light reflecting layer through the light transmissive layer.
The reflectivity in the area of the opening of the light absorptive layer is essentially that of the light reflective layer and is much greater than that of the surrounding unexposed region. During readout this difference in reflectivities is detected optically and converted into an electrical signal representative of the recorded information.
Bell, in a copending application entitled "Replicable Optical Recording Medium", Ser. No. 085,547 filed October 17, 1979 has disclosed an optical recording medium comprising a light reflective layer, a light transmissive layer and a light absorptive layer where the material comprising the light transmissive layer melts, sublimes or decomposes at a temperature at least 300.degree. C. less than that of the material which comprises the light absorptive layer. Information is recorded as openings in both the light transmissive and light absorptive layers or as bubbles in the light absorptive layer. These storage mechanisms produce topographical features which are suitable for replication, thus allowing the replication of the recorded information without additional processing steps. This recording mechanism was observed to improve the signal-to-noise performance of the recording medium for incident light beam powers just above the threshold for recording.
The cost and complexity of an optical recording system is greatly affected by the light power required to record information at an acceptable signal-to-noise ratio. Therefore, it would be desirable to have a recording medium for which the light power required to record information at an acceptable signal-to-noise ratio is significantly less than that required by the optical recording media disclosed by Bell, which decreases the cost of the system.